It is known that unsaturated aliphatic aldehyde, for example, acrolein or methacrolein, can be produced by various methods of catalytic oxidation of olefins, for example, propylene or isobutylene, in gas phase with molecular oxygen, at an elevated temperature, in the presence of various types of catalysts. For example, U.S. Pat. No. 3,522,299 discloses a method for producing acrolein in the presence of a Mo-Bi-Fe-Co-O type catalyst. This method results in the production of acrolein in a poor yield of 71.5% or less. Japanese Patent Application Publication (Kokoku) No. 52-50766 discloses a method for producing acrolein in the presence of an aluminum-containing Mo-Co-Bi-Fe-Al-O type catalyst. However, this method results in a poor yield of acrolein of 81% or less. The above-mentioned yields of acrolein are unsatisfactory for the industrial production of acrolein.
Also, various methods for producing the unsaturated aliphatic aldehydes in the presence of various types of catalysts containing titanium as a catalyst component, are disclosed in U.S. Pat. No. 3,198,751 (Sb-Ti-O type catalyst), Japanese Patent Application Publication (Kokoku) No. 43-6762 (Ti-Te-O type catalyst), Japanese Patent Application Publication (Kokoku) No. 45-8206 (W-Ti-P-Te-Ca-O type catalyst), British Pat. No. 1290198 (Ti-Fe-Ni-Bi-Mo-O type catalyst, U.S. Pat. No. 3,686,138 (Sb-Si-Ti-O type catalyst), Japanese Patent Application Publication (Kokoku) No. 47-40957 (Ti-SB-Te-Si-O type catalyst), Japanese Patent Application Publication (Kokoku) No. 48-1645 (Ni-Co-Fe-Bi-Ti-K-Mo-O type catalyst), Japanese Patent Application Publication (Kokoku) No. 51-47684 (Ni-Co-Fe-Bi-Ti-K-Mo-O type catalyst), Japanese Patent Application Publication No. 52-22359 (Mo-Bi-Ti-O type catalyst), U.S. Pat. No. 3,872,148 (Mo-Bi-W-Ti-O type catalyst) and U.S. Pat. No. 3,936,505 (Mo-Nb-Ti-O type catalyst). However, the above-mentioned titanium containing catalysts still result in a poor yield of the unsaturated aliphatic aldehydes, for instance, acrolein or methacrolein, of, at the highest, slightly more than 80%. This yield is not satisfactory for the industrial production of unsaturated aliphatic aldehydes. That is, both the conventional aluminium-containing catalysts and the conventional titanium-containing catalysts fail to convert the olefins into the unsaturated aliphatic aldehydes in a satisfactorily high yield thereof.
With respect to the conventional processes for the preparation of acrolein or methacrolein by the catalytic oxidation of propylene or isobutylene with molecular oxygen, at an elevated temperature, it is known that it is extremely difficult to increase the percent of yield of acrolein or methacrolein while maintaining the percent of selectivity to acrolein or methacrolein at a high level. Usually, when the conventional catalysts are used, the production of acrolein or methacrolein while maintaining the percent of conversion of propylene or isobutylene at a high level, results in a poor percent of selectivity to acrolein or methacrolein. This poor percent of selectivity causes the percent of yield of acrolein or methacrolein to be poor. Also, in order to produce acrolein or methacrolein in a high percent of selectivity thereto, it is necessary to maintain the percent of conversion of propylene or isobutylene at a low level. However, this low level of the percent of conversion results in a poor yield of acrolein or methacrolein.
In the industrial production of acrolein or methacrolein, it is required that the catalyst exhibit a high strength to crushing during the reaction. However, with respect to the conventional types of catalysts, it is known that the increase in the crushing strength of the catalysts results in a decrease in the percent of conversion having high crushing strengths cause the percent of yield of acrolein or methacrolein to be poor.
It is also known that the conventional types of catalysts can not produce acrolein or methacrolein at a satisfactory high level of space time yield (g/l.multidot.hr) thereof. The term "space time yield" refers to an amount (g) of the produced acrolein or methacrolein per unit time (hr) and unit amount in volume (l) of the catalyst used.
Japanese Patent Application Publication (Kokoku) No. 52-50766, (the Applications corresponding to those in the present application) discloses a Mo-Co-Bi-Fe-Al-O type catalyst containing aluminum as a catalyst component. This type of catalyst is effective for producing acrolein or methacrolein in a considerable high yield thereof. However, it is desired that this type of catalyst be further improved so as to increase the percent of yield, the space time yield and the crushing strength of the catalyst.